1. Field of the Invention
The present invention relates to a device and method that rapidly regulate fluid mass-flow over wide ranges of pressures and flow-rates. More particularly, the present invention relates to periodically modulating large amounts of gaseous or liquid mass-flow over a wide range of frequencies for the purpose of controlling the rate of turbulent mixing with another fluid. Most particularly, the present invention is an improved device and method which set up periodic mass-flow oscillations in an air or fuel jet to improve the combustion efficiencies of various combustion devices such as incinerators or jet engines.
2. Brief Description of the Related Art
In a jet of fluid that exits from a conduit to a surrounding medium of another fluid, sudden increase of the mass-flow leads to formation of well-defined vortices that dominate the boundary between the jet fluid and the surrounding fluid. Because these vortices help transport chunks of fluid over a large distance, the rate of turbulent mixing between the two fluids is closely linked to the dynamics of these vortices. One way to manipulate the dynamics of vortices is to modulate periodically the instantaneous mass-flux of the jet.
In combustion devices, actuators can be used to enhance combustion performance such as efficiency improvement, pollutant reduction, flammability extension, and instability suppression. Combustion apparatuses which use actuators have been disclosed in U.S. Pat. No. 5,428,951 (Wilson et al.). U.S. Pat. No. 5,428,951 discloses several active control devices including loudspeakers to modify the pressure field of the system or to obtain gaseous fuel flow modulations, pulsed gas jets aligned across a rearward facing step, adjustable inlets for time-variant change of the inlet area of a combustor, and solenoid-type fuel injectors for controlled unsteady addition of secondary fuel into the main combustion zone.
Active control of a compact waste incinerator has been disclosed in U.S. Pat. No. 5,361,710 (Gutmark et al.). Again, actuators were used to control burn rates within waste incinerators and affect the formation of soot or other emissions that result from standard combustion processes. This occurs with the synchronizing of the fuel injection with the intentional formation of large-scale vortices proximate to the entrance of the combustion chamber.
For actively controlling combustion, there have been several different types of actuators, which include acoustic drivers that generate pressure waves, electrodes and heating elements that use electric-energy dissipation, etc. One other type of actuators is based on modulating instantaneous mass-flux of reactants or of chemical catalyzer. For instance, electromechanical valves, electro-pneumatic valves, and magneto-strictive valves are examples of this type. In a practical device, however, an actuator has to perform over a wide range of frequencies, pressures, and flow rates to be useful. For instance in a compact waste incinerator, it is desirable to have an actuator which is able to perform in the range of frequencies between 20 and 2000 Hz, over pressures of 1 to 50 psig, and provide flow rate oscillations of at least 20 scfm (standard cubic feet per minute) to 100 scfm.
However, previously disclosed combustion systems have lacked active control devices which permit the formation of large-scale vortices in the practical ranges of operation. Additionally, the previously disclosed active control devices do not permit liquid transfers. There is a need in the art of combustion devices to provide large-scale vortices which permit combustion devices to function over a wide range of pressures, temperatures, frequencies and mass-flux rates. Additionally, there is a need for the responsiveness of active control devices to function with increased efficiencies, even at higher pressures, temperatures and mass-flux rates. Improved active control of combustion systems should also be reliable and relatively inexpensive.
Among those actuators previously listed, only an electro-pneumatic valve, which is known in the art as a Ling valve, has been able to come close to the restrictive requirement of practical combustion systems. The Ling valve comprises a plurality of interleaving stationary and magnetically movable slots that reciprocally allow passage of air through a pneumatic valve at rates and amounts defined by the electric field. The Ling valve is sold at a cost of approximately $16,000 under the trade name of EPT-1094, Electro-Pneumatic Transducer, which is manufactured by Ling Electronics Inc. of Anaheim, Calif. The Ling valve weights approximately 35 pounds, needs air cooling, and requires special inlet filters to protect the Ling valve from contamination because of the magnet field extracting ferrous particles from the fluids into the working parts of the Ling valve. The Ling valve may provide operating pressures of up to 40 psig and flow rates up to 400 scfm. The Ling valve is only operable in the low frequency range of 20 Hz to 400 Hz.
The device in the present invention is structurally different from the Ling valve. The present invention uses high-frequency-response characteristics of piezo-electric materials, large-displacement characteristics of vibrating wafers, and strategically placed valve-seat that maximizes the flow rate controllability. The device is operable over an increased range of frequencies and higher flow rates. Also, due to the simplicity of the parts and the construction design, the device is reliable and inexpensive. In combustion systems, the present device can be used to actively modulate not only the instantaneous mass-flux of the reactants within the range of specified frequencies but it can also modify mixing between fuel and oxidizer or between reactants and products by manipulating vortex dynamics of the fluid-mixing zone.